
ISE 311 Rolling lab in conjunction with Chapters 18 and 19 in the text book “Fundamentals of Modern Manufacturing” Third Edition Mikell P. Groover Prepared by: Amin Naser and Tom Yelich May 22 nd , 2008. Outline. Introduction to rolling Flat rolling and its analysis Flat rolling defects
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
ISE 311Rolling labin conjunction withChapters 18 and 19 in the text book“Fundamentals of Modern Manufacturing”Third EditionMikell P. GrooverPrepared by: Amin Naser and Tom YelichMay 22nd, 2008
Rolling is a bulk deformation process in which the thickness of the
work is reduced by compressive forces exerted by two opposing
rolls. The rolls rotate to pull and simultaneously squeeze the work
between them.
The rolling process (specifically: flat rolling)
The basic process shown in the previous figure is “Flat Rolling”,
used to reduce the thickness of a rectangular cross section. A
closely related process is “shape rolling”, in which a square cross
section is formed into a shape such as an I-beam. (in this lab, you
will only do flat rolling)
Shape Rolling
Flat Rolling
Shape Rolling
Raw material and final product both in flat and shape rolling
After casting, ingots are rolled into one of three intermediate
shapes called blooms, billets, and slabs:
In this lab, you will only do cold rolling (at room temperature).
thickness is reduced by an amount called the draft:
d = to - tf
where
d: draft
to: starting thickness
tf : final thickness
% reduction = % r = (d/ to)* 100%
w/t Ratio = initial width/ initial thickness
% Spread = (Final width-initial width)/ (initial width) *100%
L = (R * d)0.5
Where
L: approximate contact length, R: roll radius, d: draft
(See the next figure)
This figure shows the contact
length between the work and
the rolls, the initial and final
work velocities, in addition to
the velocity of the rolls:
The true strain experienced by the work in rolling is based on the
stock thickness before and after rolling:
ε = ln (to/tf)
The average flow stress in flat rolling can be can be determined
by:
Where:
K: Strength coefficient
n: Strain hardening exponent
(see the tensile testing module for more information about the power law σ = K εn)
where
Yavg, i : the average flow stress in the ith pass
: the strain after the i-1th (before the ith pass)= ln (to/ti-1)
: the strain after the ith pass = ε = ln (to/ti)
K : Strength coefficient
n : Strain hardening exponent
To calculate the roll force required to maintain separation
between the two rolls:
F = 1.15 * Yavg, i * Li * wi
where:
F : roll force
Yavg, i : the average flow stress in the ith pass
Li : the approximate contact length in the ith pass
wi : the width of the sheet in the ith pass
The torque in rolling can be estimated by:
T = 0.5 * F * L
Where:
T: Torque (lb.in or N.m)
F: Roll Force
L: Contact length
The Power required to drive the two rolls is calculated as follows:
P = 2π*N*F*L
Where:
P: Power (in J/s =Watt or in-lb/min)
N: Rolls rotational speed (RPM)
F: Roll Force
L: Contact length
From the previous equations we can conclude the following:
dmax = μ2 R
Where:
dmax : maximum draft for successful rolling
μ : coefficient of friction
R : roll radius
Defects in rolling may be either surface or structural defects:
bending of the rolls causes the sheet to be thinner at the edges, which
tend to elongate more. Since the edges are restricted by the material at the center, they tend to wrinkle and form wavy edges.
2. Center and edge cracks: caused by low material ductility and barreling of the edges.
3. Alligatoring: results from inhomogeneous deformation or defects in the original cast ingots.
Manufacturing Processes for Engineering Materials, 5th edition, S. Kalpakjian and S. Schmid
Structural defects in sheet rolling:
Wavy Edges Center cracking Edge cracking Alligatoring
Manufacturing Processes for Engineering Materials, 5th edition, S. Kalpakjian and S. Schmid
Various rolling mill configurations are available (see next figure):
Using small rolls reduces power consumption but increases the roll deflection. In this configuration, two small rolls, called working rolls, are used to reduce the power and another two, called backing rolls, are used to provide support to the working rolls.
4. Cluster rolling mill: another configuration that allows smaller working rolls to be used.
5. Tandem rolling mill: series of rolling stands .
This lab has the following objectives:
A picture of the scale-down rolling mill used in the lab:
Adjusting Screw
Rolls Housing/ Stand
Rolls
Part I: Rolling
1- Obtain the material data (K, n) from your lab instructor and record it in your datasheet.
2- Record the following initial conditions of your sample strip in the table provided:
3- Set the roll gap for the first pass (set the adjusting screw to 5)
4- Start the rolling mill
Part I: Rolling (continued)
5- Feed the strip through the mill (make sure not to feed the strip at an angle into the rolls).
6- In the table provided, record the:
7- Reduce the roll gap by one unit per pass and repeat steps 3-6 for the
remaining four passes.
Part II: Estimating the coefficient of friction
1- With a new sample, record the initial thickness.
2- Measure the roll radius.
3- Set the roll gap to 1 on the adjusting screw.
4- Start the rolling mill.
5- Very gently attempt to feed the strip through the mill, but do not force the strip into the mill. Hold the strip as level as possible and let friction between the rolls and the strip pull it in (this must be the case to get accurate data regarding the friction force). Note: the strip will not be pulled in on this first attempt.
Part II: Estimating the coefficient of friction (Continued)
6- Open the roll gap by steps on one-half units on the roll set screw and repeat step 5 until the mill just pulls in the strip. The number on which the roll is set is not important and only the initial and final thickness of the specimen are needed.
7- Record the final thickness and complete the calculations with the
formulas provided.
Part III: Transverse strains in rolling (Spread)
In this section of the lab, we will use a strip of aluminum that has lower
width to thickness ratio. This section highlights the fact that plane strain
assumptions in rolling must be used carefully and only for particular
cross-sections.
1- Record the specimen initial width and thickness.
2- The lab instructor will set the roll gap to 3
3- Roll the strip and then record the final width and thickness.
You will notice that there is a change in all dimensions.
This lab preparation material introduced: